Cellulosic fibrous calcium silicate pigment, a method of making it and a sheet of paper containing it



\ Patented June 3, 1952 UNITED STATES PATENT F F'ICEI CELDULOSIC FIBROUS CALCIUM 'SILIGATE; IIGMENT,v A. ME THOD 0F MAKING-I 1 AND- A SHEET OF PAPER CONTAINING IT William'L. Cralg,'Westport, (30am; assignor" to- B, T. Vanderbilt Company, Inc New York; N. Y a: corporation of New York No Drawing. Application December 1 0,l949, Serial No. 132, 11.70

15, Claims.

This-invention has io'r its object a g'clatlnized' cllttlOSi' fibi dlls hydrated calcium silicate pig ment and a method or producingit andnew' compo'sit'e sheets of paper made-therewithr The-new fibrous hydratedcalcium silicatepig-r merits: are highly pigmented cellulo'sic pulp fibers containing finely divided hydrated calcium silicate precipitated: largely within the fibers and on and around" the fibers in amount greatly exceeding the Weight of the fibers and advantageously several times the dry weight of the fibers.

The new fibrous pigments are produced from swollen, hydrated and gelatinized cellulosie pulp fibers containing a solublecalcium sa1t,adva'ntageously calcium chloride; largely within the fibers by reaction of a soluble, silicate therewith, particularly sodium silicate or water glass, with resultings precipitation of finely divided hydrated calcium silicate largely within the fibers as well as on. and around the fibers.

Thenew' paper made with thefibrous hydrated calcium silicate pigment is made up largely of untreated stock or fibers combined with. aregu lated amount of the highly pigmented fibrous hydrated calcium silicate pigment-.

The new fibrous pigments are made by first subjecting the fibers inithe form of a pulprto' the action of a solution of calcium chloride containing ,airamount of chloride exceeding the dry weight of thefibers, and" of a sufiicient concen-'- tration to: efiect' swelling and hydration andgelatiniz'ation of the fibers, or with a-more dilute solution'ot calcium chloride combined with mc-- chan'ical working or beating; 0'11- therpulp to eiiect swelling arid hydration and gelatinization of the fibers so that a large amount of calcium chloride willl be contained within the gelatinized fibers; and the resulting fibers are then? treated with a solution of sodium silicate to precipitate the in= soluble hydrated calcium silicate largely within the fibers and also: on and around thBYfibQI'S.

The. invention is of more or less general application: to; the treatment or cellulosic pulp fibers including: chemical, semi-chemical: or mechanical pulp fibers". commonly used in paper making, such as kraft, sulfite, and soda pulp (chemical pulp) or groundwood (mechanical pulp). The fibers treated maybe bleached. or unbleached stock and may be stock which has been previously refined abeater or r'efining engine or which may he unrefined stock or which may be subjected to beating or refining in connection with the treatment of the pulp to produce the new fibrous pigment.

Where the pulp is available treated at a 2; pulp or paper m'ill it advantageously usedin the-form ofa concentrated s't'o'ck' contaminate around 4% or 5% or'6% or more of fibers basis and" the calcium chloride is advantageously added in the form of dry calcium chlorroem amount equal to and advantageously inexcess or the Weight-Of the fibrous stock (dry basis) Thus,

- around 13% to a profound modification-ofthe cellulo's'i'c fibers takes place in a short-period; oftime; e. g t, 5 to 10 01 1 5- minutes, with proper agitatiom The) fibers become more or' less gelate ihous" and transparent in appearance. With more" dilute calcium chloride solutions prolongedbeating" of the pulp in a beater isadvantageous topromote the hydrating and gelatinizing' action and also to convert the pulp into a refinedapulpl,

Instead of) adding dry calcium chloride to? an ordinary pulp containing a small percentagaofi fibers} the treatment can be carried out by add-' mg dry pulp stock (chemical, semi-chemical or mechanical pulp) to a-more'di'lute aqueoussolue tion of calcium chloride, advantageously a; solution, and with beatingor refining ot the-pulp? to promote the action of the calcium chloridaoii the fibers and to bring about the'swelling and hy-i drating and gelatiniZiI-ig. action with resulting incorporation of a considerable amount" of, the calcium chloride within the fibers aswell as: on andaround' them.

After suchtreatment of the pulpfibers; with calcium chloride the Stock is treated with a: tionor sodium silicate (advantageously water glass) e. g.,. in the form 0153271070. or 2037; $0111 tion in suificient amount to react with, thelcalci-um chloride and precipitate insoluble hydrated. cal? cium; silicate largely withm and also: on and around the modified-fibers The amountot added sodium silicate is equal: to or somewhat moreor less thanv the amountwhichis sufficient toreact with all of the calcium chloride Witli cellulose fibers (chemical: pulp) the amount; of sodium: silicate is advantageously slightly in ex-' cess of that required toireact with all: of the calci'um chloride. With groun'dwood fibersicare shouldbe. taken in eneral to avoid an excess a slight excess of calcium chloride, or with a bufier salt.

The resulting treated and pigmented stock is highly hydrated and has little strength, or relatively much less strength than the untreated stock, but it carries the precipitated hydrated calcium silicate distributed throughout the hydrated stock While pigment is also precipitated on the hydrated stock and to a limited extent in the relatively small amount of water in which the stock is suspended, while in a swollen and gelatinized state.

The reaction of the calcium chloride and sodium silicate to form the precipitated hydrated calcium silicate also forms sodium chloride in solution and the resulting highly pigmented stock or fibrous pigment is washed to remove this salt; A large part of this salt will be removed when the fibrous pigment is filtered or the main part of the water i separated from it, but it is desirable to wash the treated stock to effect more or less complete removal of the sodium chloride. before the fibrous pigment is dried or used.. The washing of the fibrous pigment can be carried out by decantation or by washing in pulp washers with replacement of the sodium chloride solution with fresh water or by filtering the fibrous pigment and washing the stock on the passed over a filter or screen or formed into laps to form a continuous sheet from which most of the water is drained or sucked by vacuum or it is passed through pressure rolls to squeeze out as much water as possible. This gives the fibrous pigment in wet lap or sheet form for storage or shipment.

The new fibrous pigment can also be advantageously dried under regulated conditions to form a dry fibrous calcium silicate pigment. It

is important, for producing dry fibrous pigments which can be readily rehydrated and converted into pulp form with water to avoid excessive drying and the production of a bone dry product. The drying can, however, be carried out rapidly by passing the wet pigmented fibers through a v continuous drier in sheet form and drying to a point where it still contains a small amount of water, e. g., around to more or less based on the fibrous content of the pigmented fibers. Ordinary drying rolls can be used with a limited time of contact of the continuous pigmented fiber sheet with hot rolls to avoid excessive heating and drying. The wet fibrous pigment can also be broken up into lumps or into small pieces before drying. The dried product can also be broken up'into lumps or into pieces or into coarse powder form or the dried product can be formed into rolls or into laps for storage and shipment. The new fibrous pigment will contain the finely divided, precipitated calcium silicate amount greatly exceeding the weight of the fibers treated (dry basis) and advantageously in amount three or four or five times the dry weight of the fibers, or even a higher percentage, e. g., around fiber (dry basis) and 85% precipi- 4 tated. hydrated calcium silicate, or 10% fiber (dry basis) and 90% precipitated hydrated calcium silicate.

When sodium silicate having a ratio of sodium oxide to silica of approximately lNazO to 3.25SiO2 (water glass) is reacted with the calcium chloride, the hydrated calcium silicate formed has the approximate formula CaOASiOzBI-IzO and the weight of the hydrated calcium silicate is approximately three and one-half times the weight of the calcium. chloride. When the pulp is treated with an amount of calcium chloride exceeding the weight of the fibers (dry basis), the amount of hydrated calcium silicate formed will be several times the amount of calcium chloride used.

The new fibrous hydrated calcium silicate pigment is a valuable pigment for use in paper making for admixture with paper pulp. If the cellulosic fibers treated are beaten or refined prior to or during the treatment the resulting fibrous pigment is a refined pulp stock which can be added to the furnish to be used for paper making after it has been prepared, e. g., by admixing it in regulated amounts with the furnish before it goes to the paper machine. It can also advantageously be added to the beater and subjected to further refining or added to the beater near the end of the refining treatment. Where the fibrous pigment is in a dry state it can be first rehydrated by admixing it with water and forming it into a pigmented fibrous pulp and added in this form to the other pulp to be used for paper making.

The new fibrous pigment has an important ad.- vantage over ordinary pigments which are admixed with paper pulp in that it is more readily retained and losses of pigment are minimized. Although the hydrated calcium silicate is precipitated in the form of fine particles these are held by the fibers, largely within the fibers, but also on and around the fibers, so that the fibers serve as a vehicle or skeleton for the fine calcium silicate pigment particles. 7

When the new fibrous pigments are used in paper manufacture the paper can be made from the admixed stocks on Fourdrimer or cylinder machines and various kinds of paper can be made including book paper, magazine paper, newsprint, and other printing papers which are directly prepared as pigmented papers. The present invention enables a sheet of paper to be produced approachin a precoated sheet on a paper machine. In general only a small percentage of fibrous pigment on the total stock will be necessary to incorporate the required amount of pigment in the paper. For various grades of paper an amount of fibrous pigment in which the fibrous content is around 5% or 10% of the total fibers of the stock can advantageously be used.

The fibrous pigments, while fibrous in character, are so modified and weakened by the hydrating treatment and pigment precipitation therein and thereon that they are not suitable by themselves for paper manufacture. But their high pigment content makes them valuable fibrous pigments for admixture with untreated fibers. Thus, fibrous pigments containing 10% or 15% or of fibers (dry basis) and 90% or 85% or precipitated calcium silicate, are in fibrous form even though they are made up mainly of the finely divided precipitated calcium silicate. And these fibrous pigments are valuable pigments for admixture in varying amounts of, e. g., 5% or 5 102% 615 or less; depending: uponthe toting-merit desired the resulting sheet steeped 1 'Ifieinyention will be. rurt'ner: illustrated by the followingspeci-fie exampies, but it will be unuei the invention: is not limited: thereto. Thepamtsarebyweighti rammars ground-wood stock or 5% con sistency is prepared n a-beater and 20o' parts oritniastotnr ecntaining 16 arts (dry basis) of fibers is added 18 parts or di 'y'o'al'ci u'm chloride, wimagitaitibn and refined a refiner. This caleium': euierme dissolves and formsa solution which reacts withthegrour'rdwoed stock. After sewers ao iminutes the stdck is-modifiedand hydrated. and more or less gelled and 5 3 parts of sodium silicate, Na2O.3.25SiO2 (water glassi, are then-added. the form of 'a- 10% solution. The silicate reacts-rapidly with the calcium cltlfil fcfe tl' ial'i is in and on and around" the fibers and. a; sufli'cient period of'time, e; g 1 to 15 minutes, is allowed to secure full preci itation; Ihe precipitated fibrous pigment is then thoroughly Washedto removetm salt (sodium-chloride) that has'b'een formed by the reaction. The washed pigment is then passed over ascreen or filter or between rolls to form it into lap form or is dried to a moisture content of around 5 to either bydrying'in sheet form or by grinding or breaking up into smaller pieces bei'ore drying.

Example 2;-'An alpha-cellulose pulp is prepared by beating in the beater at a 6% con sistency and to 1035 parts of the resulting s-tocl; containing. 62 parts. of alpha-cellulose (dry basis) are addedlll" parts of dry calcium chloride, with continued stirring or agitation in the beater as described-in Example 1,-and then 326 parts of Sodium'silicate NazO.3.25SiOa (water glass),- are added in the formof a 10% solution and the process is continued as in Example 1.

The products of the aboveexamples contain many timesas much pigment as fiber (drybasis). With refined fibers the-fibers may have a fiufiy appearance on grinding. Although the dry product is made up mainly of pigment it is nevertheless fibrous in character, retaining in general the fibrous structure of the treated fibers but containing a large amount of precipitated pigment within and on and around the fibers.

Example 3.Bleached sulfite pulp in the form of ordinary sheets or laps is added to a 10% calcium chloride solution in a beater in amount sufficient to form a 6% stock (6% pulp, dry basis) and the stock is subjected to a beating and refining treatment until the fibers become hydrated and swollen and somewhat gelatinous in character with little free water apparent around the swollen fibers and with resulting refining of the pulp to a greater or less extent. To the resulting mixture is added a 10% sodium silicate (water glass) solution in amount sufiicient to react with the calcium chloride contained in the treated stock, and the agitation or beating is continued for a period of e. g. 10 or minutes to effect reaction of the sodium silicate with the calcium chloride and the formation of hydrated calcium silicate largely within and also on and around the modified fibers. Sodium chloride is removed from the resulting stock by filtering or washing to remove the sodium chloride. The resulting pulp is then formed into sheets or into lap form or dried to give a dry pigmented fiber. The resulting dry fibrous pigment contains around 85% of hydrated calcium silicate and around 15% of fiber (dry basis).

6 Byyarying the manic or calcium-m incej 4 used for treating-the pulp. the ox? drated calcium silicatetormed: canbe varied and fibrous pigments produced containing, 6; ea,

' inholding the finely divided"precipitated-law cilia-ted calcium silicate in aconditiem which minimizesloss of pigment; and the nitrous pigs ment can be readily incorporated with; ordinary pa er ulp stock for paper manufacture:

In the production of paper the fibrous pigments;- such as those of the above examples; are-admixed inpulp form with amuch larger proportion-of untreated pulp fibers and the stockdiluted and formed into a sheet of paper. Sheets of paper can thus be produced with larger or smaller amounts of pigment incorporated'thei 'eih.

In making mult'i-ply paper" or board the-new fibrous hydrated calciumsilicate pigment either alone or advantageously mixed with an; equal amount or varying mounts of untreated fibers can advantageously'be applied a the-outer layer or liner" of the muiti-piy; paper or board. The other layers g-ive sum'cie'nt strength to the multiply paper or board even though the outer highly pigmented layer may be lacking in strength because of the rofound modification" to which the fibers have been subjected in converting-them the highly" pigmented 'fibers or fibrous" pigment. Thus thefibrous pigment produced by the foregoing examples can housed in the form of a stool; diluted to proper consistency, e; gm; around 1%, and then suppli d to the stuff chest reg ulating box and cylinder vat for use in. making the outer layer or liner of a composite sheet of paper on a multi-cylinder machine. The multi-cylinder machine may be otherwise operated in the usual manner to form the multi-layer sheet or board which is passed through the squeeze and pressure rolls and over the driers and calenders, being given a sizing treatment on the calenders.

As illustrating the use Of the new fibrous pigments of the above examples admixed with untreated stock for making the coating layer or liner of multi-ply paper or board the highly pigmented fibers may be admixed with an equal proportion of untreated fibers and the resulting composite furnish used in a multi-cylinder machine to form the outer layer or liner of the sheet.

I claim:

1. The method of producing a pigmented and gelatinized cellulosic fibrous stock particularly adapted for admixture with unpigmented cellulosic fibrous stock in the manufacture of paper which comprises subjecting, at ordinary temperatures, an aqueous suspension of cellulosic fibers to the action of a solution of calcium chloride until the calcium chloride brings about a gelatinization of the cellulosic fibers, and adding a solution of sodium silicate to the gelatinized cellulosic fibers containing the calcium chloride to react therewith and precipitate finely-divided hydrated calcium silicate in and on the fibers, the amount of calcium chloride in the solution and the amount of sodium silicate added to the cellulosic fibers being sufiicient that the amount of precipitated hydrated calcium silicate remaining in and on duced in accordance with the method of claim' 1 in-amount of from about 5% to 25% with unpigmented cellulosic fibers, and forming a pigmented sheet of paper from the resulting admixed fibers.

6. The method according to claim 5 in which the unpigmented cellulosic fibers are chemicallytreated fibrous pulp.

7. The method according to claim 5 in which the unpigmented cellulosic fibers are groundwood.

a 8. Highly-pigmented gelatinized cellulosic fibers produced in accordance with the method of claim 1 and containing an amount of finelydivided, precipitated, hydrated calcium silicate in excess of the dry weight of the fibers.

. 9. Highly-pigmented gelatinized cellulosic fibers as defined in claim 8 in which the weight of the finely-divided, precipitated, hydrated calcium silicate is from about 3 to 9 times the dry weight of the fibers.

l0. Highly-pigmented gelatim'zed cellulosic fibers as defined in claim 8 in which the fibers are in the form of a wet lap or sheet.

, 11. Highly-pigmented cellulosic pulp comprising the dried residue of swollen, hydrated and gelatinized cellulosic fibers and an amount of finely-divided pigment in excess of the dry weight of the fibers, and not exceeding about 9 times the dry weight of the fibers, the pigment consisting of precipitated, hydrated calcium silicate; the finely-divided pigment being largely within the dried residue of the cellulosic fibers and also on and around said fibers, the finely-divided pigment within the fibers having been precipitated in situ therein by reaction of calcium chloride with sodium silicate while the calcium chloride is within the fibers while they are in a swollen, hydrated and gelatinized state, said highly-pigmented cellulosic pulp forming a pulp-like mass on admixture with water.

12. Highly-pigmented cellulosic pulp as defined in claim 11 in which the cellulosic fibers are chemically-treated fibrous pulp.

13. Highly-pigmented cellulosic pulp as defined in claim 11 in which the cellulosic fibers are groundwood.

14. Highly-pigmented cellulosic pulp as defined in claim 11 in which the amount of precipitated, hydrated calcium silicate within, on and around the fibers is from about 3 to 9 times the dry weight of the fibers.

15. A new sheet of paper made of admixed fibers, from 5% to of which are highly pigmented gelatinized cellulosic fibers as defined in claim 8 and the remainder of the fibers are ungelatinized cellulosic fibers.

WILLIAM L. CRAIG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. THE METHOD OF PRODUCING A PIGMENTED AND GELATINIZED CELLULOSIC FIBROUS STOCK PARTICULARLY ADAPTED FOR ADMIXTURE WITH UNPIGMENTED CELLULOSE FIBROUS STOCK IN THE MANUFACTURE OF PAPER WHICH COMPRISES SUBJECTING, AT ORDINARY TEMPERATURES, AN AQUEOUS SUSPENSION OF CELLULOSIC FIBERS TO THE ACTION OF A SOLUTION OF CALCIUM CHLORIDE UNTIL THE CALCIUM CHLORIDE BRINGS ABOUT A GELATINIZATION OF THE CELLULOSIC FIBERS, AND ADDING A SOLUTION OF SODIUM SILICATE TO THE GELATINIZED CELLULOSIC FIBERS CONTAINING THE CALCIUM CHLORIDE TO REACT THEREWITH AND PRECIPITATE FINELY-DIVIDED HYDRATED CALCIUM SILICATE IN AND ON THE FIBERS, THE AMOUNT OF CALCIUM CHLORIDE IN THE SOLUTION AND THE AMOUNT OF SODIUM SILICATE ADDED TO THE CELLULOSIC FIBERS BEING SUFFICIENT THAT THE AMOUNT OF PRECIPITATED HYDRATED CALCIUM SILICATE REMAINING IN AND ON THE FIBERS IS IN EXCESS OF THE WEIGHT OF THE FIBERS.
 8. HIGHLY-PIGMENTED GELATINIZED CELLULOSIC FIBERS PRODUCED IN ACCORDANCE WITH THE METHOD OF CLAIM 1 AND CONTAINING AN AMOUNT OF FINELYDIVIDED, PRECIPITATED, HYDRATED CALCIUM SILICATE IN EXCESS OF THE DRY WEIGHT OF THE FIBERS.
 15. A NEW SHEET OF PAPER MADE OF ADMIXED FIBERS, FROM 5% TO 25% OF WHICH ARE HIGHLY PIGMENTED GELATINIZED CELLULOSIC FIBERS AS DEFINED IN CLAIM 8 AND THE REMAINDER OF THE FIBERS ARE UNGELATINIZED CELLULOSIC FIBERS. 